Wireless energy transfer

ABSTRACT

An apparatus comprising monitoring circuitry configured to monitor a resonant frequency of a supply source, a receiving component, and a control unit configured to vary a resonant frequency of said receiving component, wherein the apparatus is configured to vary the resonant frequency of said receiving component in dependence of the resonant frequency of said supply source.

FIELD OF THE INVENTION

The present invention relates to wireless energy transfer, particularly,but not exclusively, to wireless energy transfer between a supply sourceand a receiving component.

BACKGROUND OF THE INVENTION

It is common practice for a portable electronic device, for example amobile telephone or a laptop computer, to be powered by a rechargeablechemical battery. Generally speaking, such a battery is releasablyconnected to the body of a portable device.

The use of a battery for supplying power to a portable electronic deviceis not ideal because the energy storage capacity of a chemical batteryis limited. As such, it is necessary for the chemical battery to berecharged at regular intervals.

In order to provide a means for recharging the battery, the portabledevice is normally supplied with a charging means for allowingelectrical energy to flow from a mains power supply to the rechargeablebattery. The charging means is usually in the form of a charger unit,which conventionally comprises an electrical plug for connecting to amains power supply socket and an electrical cable for connecting theelectrical plug to the portable device.

This is disadvantageous because, if there is no convenient mains powersupply socket, as is the case in most outdoor and public environments,the rechargeable battery will run out of power and the portable devicewill need to be switched off.

The use of such a charger unit is further disadvantageous in that itrequires a physical connection between the portable device and a mainspower supply socket. This severely restricts the movement of theportable device during charging, thereby negating the portability of thedevice.

Another type of charger unit makes use of the principle of conventional,short-range inductive coupling, which involves the transfer of energyfrom a primary inductor in a charger unit to a secondary inductor in theportable device. Such charger units are commonly used, for example, forcharging rechargeable batteries in electric toothbrushes.

Chargers utilising this type of conventional inductive coupling are ableto transfer power wirelessly and hence do not require a physicalconnection between the mains supply and the portable device. However,the maximum distance over which effective power transfer can be achievedis limited to distances of the same order of magnitude as the physicaldimensions of the inductors. For portable electronic devices, thedimensions of the inductor are limited by the size of the portableelectronic device. Accordingly, in general, at distances of anythinggreater than a few centimetres, the efficiency of energy transferbetween primary and secondary inductors is too small for this type ofpower transfer to be viable.

Therefore, as with the electrical cable discussed above, power transferusing conventional inductive coupling requires the charger unit and theportable device to be in very close proximity, meaning that the movementof the portable device is severely restricted.

In addition to the above problems associated with recharging, the use ofa chemical battery as a power supply presents a number of furtherdisadvantages. For example, rechargeable chemical batteries have alimited lifespan and tend to experience a decrease in their maximumstorage capacity as they get older. Furthermore, chemical batteries arerelatively heavy, meaning that the inclusion of a chemical battery in aportable device generally adds a significant percentage to the device'soverall weight. If the device's reliance on the chemical battery couldbe reduced, then it would be possible for portable electronic devicessuch as mobile telephones to become significantly lighter.

SUMMARY OF THE INVENTION

According to a first example of the invention, there is provided anapparatus comprising monitoring circuitry configured to monitor aresonant frequency of a supply source, a receiving component, and acontrol unit configured to vary a resonant frequency of said receivingcomponent, wherein the apparatus is configured to vary the resonantfrequency of said receiving component in dependence of the resonantfrequency of said supply source

The receiving component of the apparatus described in the immediatelypreceding paragraph may be adapted to receive energy wirelessly from thesupply source by resonant inductive coupling.

The receiving component of the apparatus described in either of theimmediately preceding paragraphs may comprise an adaptive receivingcomponent having a variable resonant frequency.

The apparatus described in any of the three immediately precedingparagraphs may be configured to match the resonant frequency of saidreceiving component with the resonant frequency of said supply source.

A voltage may be induced in the receiving component of the apparatusdescribed in any of the four immediately preceding paragraphs by amagnetic field generated by the supply source, and the control unit maybe configured to vary the resonant frequency of the receiving componentto match the resonant frequency of the supply source.

The apparatus described in any of the four immediately precedingparagraphs may further comprise a plurality of electrical components,and the apparatus may be configured to supply electrical energy to atleast one of these electrical components.

The apparatus described in the immediately preceding paragraph mayfurther comprise a battery for supplying electrical energy to at leastone of the electrical components when energy is not being received fromthe supply source.

The apparatus described in any of the preceding paragraphs may comprisea portable electronic device.

The apparatus described in any of the preceding paragraphs may comprisea mobile telephone, personal digital assistant (PDA) or laptop computer.

According to a second example of the invention, there is provided anapparatus comprising means for detecting a presence of a supply source,means for monitoring a resonant frequency of said supply source, andmeans for varying a resonant frequency of a receiving component independence of the resonant frequency of said supply source.

According to a third example of the invention, there is provided anapparatus comprising a receiving component having variable resonancecharacteristics for receiving energy wirelessly from a supply source,wherein the resonance characteristics of the receiving component may bevaried to match resonance characteristics of the supply source toincrease the efficiency at which energy is received from the supplysource.

The apparatus described in the immediately preceding paragraph mayfurther comprise monitoring circuitry for detecting and monitoring theresonance characteristics of the supply source.

The receiving component of the apparatus described in either of the twoimmediately preceding paragraphs may comprise an adaptive receivingcomponent having variable resonance characteristics and the apparatusmay further comprise a control unit configured to automatically vary theresonance characteristics of the adaptive receiving component to matchthe resonance characteristics of the supply source.

The apparatus described in any of the three immediately precedingparagraphs may further comprise one or more electrical components andthe receiving component may be coupled to power supply circuitry tosupply power to at least one of these electrical components.

The apparatus described in the immediately preceding paragraph mayfurther comprise a battery for supplying electrical energy to at leastone of the electrical components when energy is not being received fromthe supply source.

The apparatus described in any of the five immediately precedingparagraphs may comprise a portable electronic device.

The apparatus described in any of the six immediately precedingparagraphs may comprise a mobile telephone, personal digital assistant(PDA) or laptop computer.

According to a fourth example of the invention, there is provided asystem comprising a supply source, and an apparatus comprisingmonitoring circuitry configured to monitor a resonant frequency of thesupply source, a receiving component, and a control unit configured tovary a resonant frequency of said receiving component, wherein theapparatus is configured to vary the resonant frequency of said receivingcomponent in dependence of the resonant frequency of said supply source.

According to a fifth example of the invention, there is provided amethod comprising detecting a presence of a supply source, monitoring aresonant frequency of said supply source, and varying a resonantfrequency of a receiving component in dependence of the resonantfrequency of said supply source.

The method described in the immediately preceding paragraph may furthercomprise matching the resonant frequency of said receiving componentwith the resonant frequency of said supply source.

The method described in either of the two immediately precedingparagraphs may further comprise receiving energy wirelessly at thereceiving component from the supply source by resonant inductivecoupling.

The receiving component of the method described in any of the threeimmediately preceding paragraphs may comprise an adaptive receivingcomponent having a variable resonant frequency and the method mayfurther comprise inducing a voltage in the adaptive receiving componentusing a magnetic field generated by the supply source, and varying theresonant frequency of the adaptive receiving component to match theresonant frequency of the supply source.

The method described in any of the four immediately preceding paragraphsmay further comprise supplying electrical energy to an electricalapparatus.

The method of the immediately preceding paragraph may further comprisesupplying energy to at least one component of an electrical device froma battery when energy is not being received at the receiving componentfrom the supply source.

The method of the paragraph six paragraphs above this one may furthercomprise receiving energy at the receiving component from the supplysource by resonant inductive coupling, and supplying energy received byresonant inductive coupling to at least one component of an electricaldevice.

According to a sixth example of the invention, there is provided acomputer program stored on a storage-medium which, when executed by aprocessor, is arranged to perform a method comprising detecting apresence of a supply source, monitoring a resonant frequency of saidsupply source, and varying a resonant frequency of a receiving componentin dependence of the resonant frequency of said supply source.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more fully understood, embodimentsthereof will now be described by way of illustrative example withreference to the accompanying drawings in which:

FIG. 1 is a diagram showing a flow of energy from a feeding device to aportable electronic device.

FIG. 2 is a circuit diagram of primary and secondary RLC resonatorcircuits with coupling coefficient K.

FIG. 3 is a circuit diagram of an equivalent transformer circuit for thefirst and second RLC resonator circuits shown in FIG. 2.

FIG. 4 is a circuit diagram of a reduced circuit of the equivalenttransformer circuit shown in FIG. 3.

FIG. 5 shows the impedances of the individual components of theequivalent transformer circuit shown in FIG. 3.

FIG. 6 is a graphical illustration of the relationship between theefficiency of power transfer between two resonators and the differencebetween the resonators' resonant frequencies.

FIG. 7 is an illustration of a wireless transfer of energy from afeeding device to a portable electronic device at mid-range usingconventional inductive coupling.

FIG. 8 is an illustration of a wireless transfer of energy from afeeding device to a portable electronic device at mid-range usingresonant inductive coupling.

FIG. 9 is a schematic diagram of a portable electronic device, includinga reactance and monitoring circuitry.

FIG. 10 is a schematic diagram showing components of a wireless powertransfer apparatus in a portable electronic device.

FIG. 11 is a schematic diagram showing an adaptive receiving componentin a wireless power transfer apparatus of a portable electronic device.

FIG. 12 is a flow diagram showing steps associated with the initiationof wireless power transfer by resonant inductive coupling.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a feeding device 100 comprises a supply source 110for supplying power wirelessly to a portable electronic device 200. Thesupply source 110 comprises a primary reactance, for example comprisinga primary inductor 111, adapted to receive an electrical current from anelectrical circuit 112. The electrical circuit 112 may be optionallyconnected to a power supply, for example comprising a mains power supply300, for supplying electrical current to the electrical circuit 112. Theprimary inductor 111 has an inductance L₁₁₁, Q-factor Q₁₁₁ and resonantfrequency f₀₍₁₁₁₎.

As will be understood by a skilled person, a flow of electrical currentthrough the primary inductor 111 causes a magnetic field 400 to becreated around the primary inductor 111. As is shown by FIG. 1, themagnetic field 400 created around the inductor 111 penetrates theexterior of the feeding device 100, meaning that the effects of themagnetic field 400 may be experienced in the surrounding environment.For instance, the magnetic field 400 may be used to induce a voltage ina receiving component comprising a secondary reactance, such as asecondary inductor in an electrical device. This is the principle uponwhich wireless energy transfer through conventional short-rangeinductive coupling is based. However, efficient wireless energy transferby such conventional short-range inductive coupling is limited todistances of the same order of magnitude as the physical dimensions ofthe inductors involved in the energy transfer.

As is fully described below, the portable electronic device 200 isadapted to receive energy wirelessly by an alternative type of inductivecoupling. This alternative type of inductive coupling will be referredto as resonant inductive coupling.

Using resonant inductive coupling, is it possible to efficientlytransfer energy over longer distances than over those possible withconventional inductive coupling. This means that resonant inductivecoupling provides a greater degree of freedom and flexibility thanconventional inductive coupling when used for the transfer of energy. Asis described in more detail below, resonant inductive coupling is basedon inductive coupling in which the resonant frequency f₀ of a supplysource and the resonant frequency f₀ of a receiving component are equalto one another.

More specifically, if the resonant frequency f₀ associated with aprimary reactance, for example the resonant frequency f₀₍₁₁₁₎ associatedwith the inductor 111 in the feeding device 100, is equal to theresonant frequency f₀ associated with a secondary reactance, for examplea receiving component comprising a secondary inductor in a portableelectronic device 200, placed in a magnetic field generated by theprimary reactance, efficient wireless energy transfer between theprimary and secondary reactances can be achieved at longer ranges thanis possible with conventional inductive coupling.

For example, wireless energy transfer with an efficiency of tens ofpercent may be achieved by resonant inductive coupling over distances atleast one order of magnitude greater than the physical dimensions of theinductors being used for the transfer.

A general example of wireless energy transfer between two inductors byresonant inductive coupling is given below.

Referring to FIG. 2, there are shown primary and secondary RLC resonatorcircuits 500, 600. The primary RLC circuit 500 comprises a firstinductor (L₁) 510, a first capacitor (C₁) 520 and a first resistor (R₁)530. The secondary RLC circuit 600 comprises a second inductor (L₂) 610,a second capacitor (C₂) 620 and a second resistor (R₂) 630. In thisexample, L₁=L₂ and C₁=C₂.

The primary RLC circuit 500 is connected to a power source, comprising atime-dependent current source (i_(SUPPLY)(t)) 540. The time-dependencyof the current source 540 is such that the current may take the form ofa sine wave, tuned to the resonant frequency

$f_{0} = {\frac{1}{2\pi \sqrt{L_{1}C_{1}}} = \frac{1}{2\pi \sqrt{L_{2}C_{2}}}}$

of both the first and second RLC circuits 500, 600.

The second RLC circuit 600 is connected to a load, represented in FIG. 2as a DC current source (i_(LOAD)) 640. The current from the DC currentsource 640 is zero when energy is not being transferred between thefirst and second RLC circuits 500, 600.

The Q-values associated with the first and second resonator circuits500, 600 are represented by the first and second resistors 530, 630. Asis explained in more detail below, the magnitude of the Q-values of theresonator circuits 500, 600 is proportional to the efficiency of energytransfer between the circuits 500, 600.

In this general example, the inductors 510, 610 are separated by adistance approximately one order of magnitude greater than the physicaldimensions of the inductors 510, 610 themselves. At this range, thecoupling coefficient K between the inductors 510, 610 is small, forexample 0.001 or less, meaning that any attempt to transfer energybetween the resonator circuits 500, 600 by conventional inductivecoupling would be extremely inefficient.

FIG. 3 shows an equivalent transformer circuit for the first and secondRLC resonator circuits 500, 600. When the frequency of thetime-dependent current source 540 is not equal to the resonant frequencyf₀ of the second RLC resonator circuit 600, the second resonator circuitis bypassed due to negligible inductance LK. As such, very little or nopower is transferred to the load. However, when the conditions forresonant inductive coupling are met, this situation is reversed as isexplained below.

A first condition for energy transfer by resonant inductive coupling isthat the Q-values (represented by the resistors 530, 630) of theresonator circuits 500, 600 are very high, for example one hundred ormore. A second condition for energy transfer by resonant inductivecoupling is that the resonant frequencies f₀ of the circuits 500, 600are equal to one another. When these conditions are met, and current issupplied by the current source 540 at

${f_{0} = \frac{1}{2\pi \sqrt{L_{1}C_{1}}}},$

current in the first inductor 510 is routed via the second inductor 610.Under these conditions, the inductance LK in the equivalent transformercircuit shown in FIG. 3 is tuned with the secondary resonator circuit.As such, the equivalent transformer circuit shown in FIG. 3 can bereduced to the circuit of a single electrical resonator, as shown byFIG. 4. There is no limit on the number of secondary resonator circuitswhich could receive current from a primary resonator circuit in thisway.

The impedances of the individual components of the equivalenttransformer circuit shown in FIG. 3 are shown in FIG. 5. The impedance Zof the reduced circuit can thus be calculated as follows:

$Z = \frac{{j\omega}\; L\; {K \cdot Z_{secondary}}}{{{j\omega}\; L\; K} + Z_{secondary}}$

Assuming the Q-value of the secondary resonator circuit 600 is high,Z_(secondary) may be written as:

$Z_{secondary} = {{{{j\omega}\; {L( {1 - K} )}} + {{1/{j\omega}}\; C}}\therefore \begin{matrix}{Z = \frac{j\; \omega \; L\; {K \cdot ( {{{j\omega}\; {L( {1 - K} )}} + {{1/{j\omega}}\; C}} )}}{{{j\omega}\; L\; K} + ( {{{j\omega}\; {L( {1 - K} )}} + {{1/{j\omega}}\; C}} )}} \\{= \frac{{j\omega}\; L\; {K \cdot ( {{{j\omega}\; {L( {1 - K} )}} - {{j\omega}\; L}} )}}{{{j\omega}\; L\; K} + ( {{{j\omega}\; {L( {1 - K} )}} - {{j\omega}\; L}} )}} \\{= \frac{{j\omega}\; L\; {K \cdot ( {{- {j\omega}}\; L\; K} )}}{{{j\omega}\; L\; K} - {{j\omega}\; L\; K}}}\end{matrix}}$

∴|Z|→∞ as the conditions for resonant inductive coupling are reached.

In this way, a secondary resonator circuit may be tuned so as to receiveenergy by resonant inductive coupling from any primary resonatorcircuit.

FIG. 6 illustrates a general relationship between the efficiency ofwireless energy transfer η through inductive coupling between primaryand secondary reactances separated by a distance one order of magnitudelarger than the physical dimensions of the reactances. The efficiency ofwireless energy transfer η is plotted on the vertical axis using alogarithmic scale, and the difference in resonant frequency f₀ betweenthe reactances is plotted on the horizontal axis. This relationship isapplicable to, for example, wireless energy transfer between the primaryinductor 111 of the feeding device 100 and a secondary inductor 211 of aportable device 200 shown in FIG. 7.

As can be seen, the efficiency of wireless energy transfer η between thereactances is at a maximum when the resonant frequencies f₀ associatedwith the reactances are equal to one another. Moreover, the efficiencyof wireless energy transfer η between the reactances decreases markedlyas the difference between the resonant frequencies f₀ associated withthe reactances increases. Accordingly, as discussed above, in order totransfer energy at the maximum possible efficiency it is preferable forthe reactances to have resonant frequencies f₀ which are as close toeach other as possible. Ideally, the resonant frequencies f₀ should beidentical.

In addition, as previously discussed, the efficiency of energy transferbetween primary and secondary reactances is proportional to themagnitude of the Q-values associated with the reactances; for a highefficiency of energy transfer, the magnitude of the Q-values should belarge. For example, in the case of the primary and secondary inductors111, 211 discussed above in relation to the transfer of energy from thefeeding device 100 to the portable device 200, efficient energy transfermay be achieved with Q-values Q₁₁₁, Q₂₁₁ in the order of 100.Furthermore, the relative difference between the resonant frequenciesf₀₍₁₁₁₎, f₀₍₂₁₁₎ associated with the inductors 111, 211 should be lessthat the reciprocal of their associated Q-values. At relativedifferences greater than the reciprocal of the Q-values, the efficiencyof energy transfer decreases by 1/Q².

FIGS. 7 and 8 illustrate the difference between conventional inductivecoupling and resonant inductive coupling when the distance betweenreactances, for example the primary and secondary inductors 111, 211, isone order of magnitude greater than the reactances' physical dimensions.Referring to FIG. 7, with conventional inductive coupling, i.e. when thedifference between the resonant frequencies associated with theinductors 111, 211 is outside of the limits discussed above, only anegligible amount of energy in the magnetic field 400 is passed from theprimary inductor 111 to the secondary inductor 211 in the portabledevice 200. In contrast, referring to FIG. 8, when the resonantfrequencies f₀ associated with the inductors 111, 211 are matched,energy is able to tunnel by resonant inductive coupling from the primaryinductor 111 in the feeding device 100 to the secondary inductor 211 inthe portable electronic device 200 via the magnetic field 400.

For the purposes of simplicity and clarity, the above example discussesthe transfer of energy from a primary inductor 111 to a single secondaryinductor 211. However, alternatively, energy can be transferred from theprimary inductor 111 to a plurality of secondary inductors 211 all beingassociated with the same resonant frequency f₀, potentially enablingmultiple portable devices 200 to receive energy wirelessly from a singlefeeding device 100.

In this way, feeding devices 100 are able to supply energy to portableelectronic devices 200 over mid-ranges, for example several metres, inenvironments in which it is not convenient to install mains powersockets. As an example, in a similar manner to the installation ofwireless LANS in cafés and restaurants, a network 700 of feeding devices100 could be installed throughout a public space to provide members ofthe public with a power supply for their portable electronic devices200. Such a public space could be, for example, a café, restaurant, bar,shopping mall or library. Alternatively, feeding devices may beinstalled in private spaces such as, for example, the interior of aperson's car or home.

In order to maximise the potential of such a network 700 of feedingdevices 100, it is preferable that the feeding devices 100 have thecapacity to supply energy to as many portable devices 200 as possible.One way in which this could be achieved is to implement a degree ofstandardization in the properties of the reactances, for example theprimary and secondary inductors 111, 211, used in the feeding devices100 and portable electronic devices 200. In particular, it would bepreferable if the resonant frequency f₀ associated with the primaryreactance in each feeding device 100 of the network 700 was the same.This would enable manufacturers of portable devices 200 and otherelectrical devices to equip their devices with secondary reactancesassociated with the same standardized resonant frequency f₀.

A skilled person will appreciate, however, that due to manufacturingtolerances, the mass production of inductors to a degree of accuracy inwhich all the inductors are associated with exactly the same resonantfrequency f₀ may be difficult to achieve. This will lead to variationsin both the resonant frequencies f₀ of feeding devices 100, and tovariations in the resonant frequencies f₀ of portable devices 200.Furthermore, even if feeding devices 100 and portable devices 200 can bemanufactured with identical resonant frequencies f₀ in free space, theresonant frequencies f₀ of each individual unit will be affected when inuse by other inductors in the unit's surrounding environment. The amountby which the resonant frequency of each unit is altered will depend onthe number and proximity of other inductors.

Thus, even when attempts have made to standardize the resonantfrequencies f₀ of feeding devices and portable devices, manufacturingintolerances and environmental conditions still have the potential tocause problems for energy transfer by resonant inductive coupling.

One way to alleviate this problem is to provide portable electronicdevices 200 with a wireless energy transfer apparatus 210 for alteringthe resonant frequency f₀ associated with their secondary inductors 211post-manufacture in dependence of the properties of a nearby feedingdevice 100. This provides portable electronic devices 200 with theability to tune their inductor's resonant frequency f₀ to match thatassociated with the primary inductor 111 in a nearby feeding device 100and thus receive energy wirelessly by resonant inductive coupling.

An exemplary embodiment of a portable electronic device 200 adapted toreceive energy wirelessly by resonant inductive coupling is given below.Referring to FIG. 9, the portable electronic device 200 comprises awireless energy transfer apparatus 210, comprising a power supply unit(PSU), for receiving energy from a magnetic field and supplyingelectrical energy to electrical components 240 of the portable device200. Alternatively, as discussed below, electrical energy may besupplied to a rechargeable chemical battery 250 of the portableelectronic device 200.

In the example discussed below, the magnetic field will be referred toin the context of the magnetic field 400 created by current flowingthrough the primary inductor 111 in a feeding device 100. However, askilled person will appreciate that the magnetic field couldalternatively correspond to a magnetic field created by another feedingdevice, or any other suitable magnetic field source.

The wireless energy transfer apparatus 210 is controlled by amicrocontroller 220 and comprises a receiving component 211 a,comprising at least one reactance, for receiving energy wirelessly fromthe magnetic field 400 by resonant inductive coupling. In this example,the receiving component 211 a comprises a secondary inductor 211. Theinductor 211 is associated with an inductance L₂₁₁, Q-factor Q₂₁₁ andresonant frequency f₀₍₂₁₁₎. The microcontroller 220 may be integratedinto the energy transfer apparatus 210.

The wireless energy transfer apparatus 210 further comprises monitoringcircuitry 230 configured to detect a magnetic field 400 created by theprimary inductor 111 in the feeding device 100, as is described in moredetail below. Upon detecting the magnetic field 400, the monitoringcircuitry 230 and microcontroller 220 are further configured to detectand monitor the resonant frequency f₀₍₁₁₁₎ associated with the primaryinductor 111.

The features of the monitoring circuitry 230 allow the portable device200 to wirelessly receive energy over mid-range distances, for exampledistances at least one order of magnitude greater than the physicaldimensions of the primary and secondary inductors 111, 211.

Referring to FIG. 10 in combination with FIG. 9, the secondary inductor211 of the wireless energy transfer apparatus 210 has a parasiticcapacitance C and is connected to a plurality of switched-mode powersupplies (SMPSs) 212 via a diode-bridge 213 and LC filter 214. Thepurpose of the LC filter 214 is to ensure that a constant reactive loadis introduced to the secondary inductor 211. If the inductor 211 were tobe loaded resistively, there would be a significant decrease in theQ-value Q₍₂₁₁₎ associated with the inductor 211, which would in turnsignificantly reduce the efficiency of the transfer of energy from thefeeding device 100, as previously discussed.

The diode-bridge 213 and LC filter 214 also protect the inductor 211from direct exposure to the strongly time-varying load presented by theSMPSs 212, which are configured to supply power received from themagnetic field 400 to various circuits of the portable electronic device200. The SMPSs 212 may be configured, for example, to supply power to arechargeable chemical battery 250 of the portable electronic device 200,as shown in FIG. 9, for recharging.

Alternatively the SMPSs 212 may be configured to supply power directlyto electrical components 240 of the portable electronic device 200, withthe chemical battery 250 acting as a reserve power source. For example,the chemical battery 250 may be configured only to supply power toelectrical components 240 of the portable electronic device 200 when thewireless energy transfer apparatus 210 is not receiving power byresonant inductive coupling. If feeding devices 100 were to becomewidespread, the inclusion of the rechargeable battery 250 in theportable device 200 could become unnecessary.

Referring to FIG. 11, in this example of the portable electronic device200, the receiving component 211 a is adaptive. This allows theresonance characteristics associated with the secondary inductor 211 tobe tuned to match the resonance characteristics associated with theprimary inductor 111 in the feeding device 100. This provides the degreeof tuneability necessary for the resonant frequency f₀₍₂₁₁₎ associatedwith the secondary inductor 211 to be varied, should the resonantfrequency f₀₍₂₁₁₎ not be identical to that associated with the primaryinductor 111 in the feeding device 100.

In more detail, as is shown by FIG. 11, the receiving component 211 acomprises the secondary inductor 211 optionally coupled to an array ofcapacitors 215, each capacitor 215 having a different capacitance toeach of the others. For example, as shown by FIG. 11, the capacitors 215may comprise N capacitors with capacitances C₀, C₀/2, . . . C₀/2^(N−1).Each of the capacitors 215 may be optionally coupled to the secondaryinductor 211 to affect the capacitance C₂₁₁ of the receiving component211 a, thereby varying the resonant frequency f₀₍₂₁₁₎ associated withthe inductor 211 and providing a mechanism for the portable device 200to match the resonant frequency f₀₍₂₁₁₎ associated with the secondaryinductor 211 with the resonant frequency f₀₍₁₁₁₎ associated with theprimary inductor 111 in the feeding device 100. It will be appreciatedthat the resonant frequency f₀₍₂₁₁₎ associated with the secondaryinductor 211 could alternatively be varied by altering the inductance ofthe receiving component 211 a.

In this implementation, as is shown by FIG. 11, the array of capacitors215 is coupled to a control unit 216 in the microcontroller 220 forautomatically controlling the capacitance C₂₁₁ of the receivingcomponent 211 a in dependence of a control signal from the monitoringcircuitry 230. The microcontroller 220 may comprise a memory and signalprocessing means 217, for example including a microprocessor 218,configured to implement a computer program for detecting and monitoringthe resonant frequency associated with the primary inductor 111 throughthe monitoring circuitry 230 and analysing the control signal from themonitoring circuitry 230 to vary the resonant frequency associated withthe secondary inductor 211 by connecting and disconnecting theindividual capacitors 215.

In this way, the control unit 216 is able to adapt the resonantfrequency f₀₍₂₁₁₎ associated with the secondary inductor 211 to make itequal to the resonant frequency f₀₍₁₁₁₎ associated with the primaryinductor 111, thereby initiating resonant inductive coupling between theprimary inductor 111 and the secondary inductor 211.

The monitoring circuitry 230 may be coupled to an output from the LCfilter 214 to detect signals from the secondary inductor 211 and thus todetect when the portable electronic device 200 is in the presence of amagnetic field 400. For example, the output of the LC filter 214 may becoupled to an input of an AD converter 231, which may be integrated intothe microcontroller 220, for sensing a voltage induced in the secondaryinductor 211 and for supplying corresponding signals to themicrocontroller 220 for calculating the resonant frequency associatedwith the primary inductor 111. The resonant frequency associated withthe secondary inductor 211 may then be varied to match the calculatedresonant frequency of the primary inductor 111.

Alternatively, as shown by FIG. 9, the monitoring circuitry 230 maycomprise a separate coil 232 for supplying induced voltage signals tothe AD converter 231.

The monitoring circuitry 230 is sensitive to very small inducedvoltages, for example of the order of microvolts, and thus is configuredsuch that it is able to detect a magnetic field 400 even when thesecondary inductor 211 is in a detuned state. The monitoring circuitry220 is thus able to detect the presence of a primary inductor 111 evenwhen then the resonant frequency f₀₍₁₁₁₎ associated with the primaryinductor 111 is not equal to the resonant frequency f₀₍₂₁₁₎ set for thesecondary inductor 211 in the portable electronic device 200.

As shown by FIG. 11, the wireless energy transfer apparatus 210 mayinclude a memory 219 for storing frequency values corresponding toresonant frequencies f₀ in different environments, such that theresonant frequency associated with the secondary inductor 211 can beautomatically adjusted upon the portable electronic device 200 enteringa particular environment. For example, such automatic adjustment couldbe prompted by a control signal, received through an aerial of theportable device 200, indicating that the device 200 has entered afamiliar environment. The memory 219 may also be suitable for storingtuning values between various life cycle states. The memory 219 maycomprise non-volatile memory in order that the various resonantfrequency values f₀ stored in the memory 219 are not lost when thedevice 200 is switched-off.

Steps associated with the initiation of a wireless energy transferbetween a supply source 110, for example comprising a primary inductor111, and the portable electronic device 200 in the manner describedabove are shown in FIG. 12.

Referring to FIG. 12, as described above, the first step S1 is to detectthe presence of the supply source 110 by detecting the presence of itsassociated magnetic field 400 from an induced voltage at the monitoringcircuitry 230. The supply source 110 may comprise a primary inductor 111in a feeding device 100. The second step S2 is to calculate and monitorthe resonant frequency of the supply source 110, and the third step S3is vary the resonant frequency of the receiving component 211 a,comprising the secondary inductor 211, in dependence of the resonantfrequency of the supply source 110. In order to initiate wireless energytransfer with the highest possible efficiency, the third step S3involves matching the resonant frequency of the receiving component 211a with the resonant frequency of the supply source 110. Upon completingthese steps, the fourth step S4 is to receive energy wirelessly from thesupply source 110 at the receiving component 211 a by resonant inductivecoupling, and the fifth step S5 is to supply the energy to one or morecomponents 240 of the portable device 200.

If wireless energy transfer between the supply source 110 and portabledevice 200 stops, for example because the portable device 200 moves outof range, then, as described above, the chemical battery 250 may beconfigured to supply electrical energy to the components 240 of theportable device 200 in step S6. As shown by FIG. 12, in step S7, thesupply of electrical energy from the battery 250 is ceased when wirelessenergy transfer by resonant inductive coupling is reinitiated.

The above example discusses the use of an adaptive receiving component211 a to vary the resonant frequency associated with the secondaryinductor 211 in a portable electronic device 200 so as to match theresonant frequency associated with the secondary inductor 211 to adetected resonant frequency associated with a primary inductor 111 in afeeding device 100. However, it will be appreciated that an adaptivecomponent could alternatively be employed in a feeding device 100 so asmatch the resonant frequency associated with a primary inductor in thefeeding device 100 to that of a secondary inductor in a portableelectronic device.

For example, a portable electronic device 200 may be configured tosupply a control signal to a feeding device 100 in order to supply thefeeding device 100 with the resonance characteristics of the secondaryinductor in the portable electronic device. The feeding device 100 wouldthen be able to match the resonant frequency associated with its primaryinductor to the resonant frequency associated with the secondaryinductor in the portable device 200, thereby initiating wireless energytransfer by resonant inductive coupling.

In another alternative, the supply source of a feeding device maycomprise a primary inductor driven by an amplifier, and themicrocontroller of the portable electronic device may be configured tomatch a resonant frequency of the adaptive receiving component to adetected frequency of a magnetic field associated with the supplysource.

In the example discussed above, the portable device 200 comprises amobile telephone or PDA. However, it will be appreciated that theportable device may alternatively comprise any number of other devices,for example a laptop computer or digital music player. It will furtherbe appreciated that the invention is not limited to the supply of powerto portable electronic devices, but may be used for powering a widevariety of other electrical devices. For example, a network of feedingdevices may be installed in the home for supplying power to electriclamps and other household appliances. The above-described embodimentsand alternatives may be used either singly or in combination to achievethe effects provided by the invention.

1. An apparatus comprising: monitoring circuitry configured to monitor aresonant frequency of a supply source; a receiving component; and acontrol unit configured to vary a resonant frequency of said receivingcomponent, wherein the apparatus is configured to vary the resonantfrequency of said receiving component in dependence of the resonantfrequency of said supply source.
 2. An apparatus according to claim 1,wherein the receiving component is adapted to receive energy Tirelesslyfrom the supply source by resonant inductive coupling.
 3. An apparatusaccording to claim 2, wherein the apparatus further comprises aplurality of electrical components, and the apparatus is configured tosupply electrical energy to at least one of these electrical components.4. An apparatus according to claim 3, further comprising a battery forsupplying electrical energy to at least one of the electrical componentswhen energy is not being received from the supply source.
 5. Anapparatus according to claim 1, wherein the receiving componentcomprises an adaptive receiving component having a variable resonantfrequency.
 6. An apparatus according to claim 1, wherein the apparatusis configured to match the resonant frequency of said receivingcomponent with the resonant frequency of said supply source.
 7. Anapparatus according to claim 1, wherein a voltage is induced in thereceiving component by a magnetic field generated by the supply source,and the control unit is configured to vary the resonant frequency of thereceiving component to match the resonant frequency of the supplysource.
 8. An apparatus according to claim 1, wherein the apparatuscomprises a portable electronic device.
 9. An apparatus according toclaim 1, wherein the apparatus comprises a mobile telephone.
 10. Anapparatus according to claim 1, wherein the apparatus comprises apersonal digital assistant (PDA).
 11. An apparatus according to claim 1,wherein the apparatus comprises a laptop computer.
 12. An apparatuscomprising: means for detecting a presence of a supply source; means formonitoring a resonant frequency of said supply source; and means forvarying a resonant frequency of a receiving component in dependence ofthe resonant frequency of said supply source.
 13. An apparatuscomprising a receiving component having variable resonancecharacteristics for receiving energy wirelessly from a supply source,wherein the resonance characteristics of the receiving component may bevaried to match resonance characteristics of the supply source toincrease the efficiency at which energy is received from the supplysource.
 14. An apparatus according to claim 13, further comprisingmonitoring circuitry for detecting and monitoring the resonancecharacteristics of the supply source.
 15. An apparatus according toclaim 13, wherein the receiving component comprises an adaptivereceiving component having variable resonance characteristics and theapparatus further comprises: a control unit configured to automaticallyvary the resonance characteristics of the adaptive receiving componentto match the resonance characteristics of the supply source.
 16. Anapparatus according to claim 13, wherein the apparatus further comprisesone or more electrical components and the receiving component is coupledto power supply circuitry to supply power to at least one of theseelectrical components.
 17. An apparatus according to claim 16, furthercomprising a battery for supplying electrical energy to at least one ofthe electrical components when energy is not being received from thesupply source.
 18. An apparatus according to claim 13, wherein theapparatus comprises a portable electronic device.
 19. An apparatusaccording to claim 13, wherein the apparatus comprises a mobiletelephone.
 20. An apparatus according to claim 13, wherein the apparatuscomprises a personal digital assistant (PDA).
 21. An apparatus accordingto claim 13, wherein the apparatus comprises a laptop computer.
 22. Asystem comprising: a supply source; and an apparatus comprising:monitoring circuitry configured to monitor a resonant frequency of thesupply source; a receiving component; and a control unit configured tovary a resonant frequency of said receiving component, wherein theapparatus is configured to vary the resonant frequency of said receivingcomponent in dependence of the resonant frequency of said supply source.23. A method comprising: detecting a presence of a supply source;monitoring a resonant frequency of said supply source; and varying aresonant frequency of a receiving component in dependence of theresonant frequency of said supply source.
 24. A method according toclaim 23, further comprising: matching the resonant frequency of saidreceiving component with the resonant frequency of said supply source.25. A method according to claim 23, further comprising: receiving energywirelessly at the receiving component from the supply source by resonantinductive coupling.
 26. A method according to claim 23, wherein saidreceiving component comprises an adaptive receiving component having avariable resonant frequency and the method further comprises: inducing avoltage in the adaptive receiving component using a magnetic fieldgenerated by the supply source; and varying the resonant frequency ofthe adaptive receiving component to match the resonant frequency of thesupply source.
 27. A method according to claim 23, further comprisingsupplying electrical energy to an electrical apparatus.
 28. A methodaccording to claim 23, further comprising: receiving energy at thereceiving component from the supply source by resonant inductivecoupling; supplying energy received by resonant inductive coupling to atleast one component of an electrical device; and supplying energy to atleast one component of an electrical device from a battery when energyis not being received at the receiving component from the supply source.29. A computer program product comprising a computer-readable mediumhaving computer-readable program code embodied in said medium,comprising: a computer-readable program code configured to detect apresence of a supply source; a computer-readable program code configuredto monitor a resonant frequency of said supply source; and acomputer-readable program code configured to vary a resonant frequencyof a receiving component in dependence of the resonant frequency of saidsupply source.